Electromagnetic transducer-detector



A ril 12, 1955 J. MILLER v2,706,245

ELECTROMAGNETIC TRANSDUCER-DETECTOR Filed Feb. 24, 1950 RE AMPL/F/fR h REAMPL/F/ER .lh L

I N V EN TOR.

ATTORNEYS.

United States Patent ELECTROMAGNETIC TRANSDUCER-DETECTOR Joseph L. Miller, South Haven, Mich.

Application February 24, 1950, Serial No. 146,099

8 Claims. (Cl. 250-40) My invention relates to an improved electromagnetic transducer operative to produce sound or other waves in response to the modulations of a high frequency current.

It has heretofore been considered necessary as a practical matter to detect or demodulate high frequency signals and then separately amplify the demodulated signal for application to an electromagnetic transducer. In broadcast radio receivers, for example, the radio frequency signals vary from 550 to 1500 kilocycles having amplitude modulation with a frequency range up to about 10 kilocycles. The modulated radio frequency signals are amplified in relatively low power stages and then applied to a detector that produces the demodulated time varying signal having frequency components up to about 10 kilocycles. This signal is then amplified anew to bring it to a level satisfactory for loud speaker operation.

The foregoing steps necessarily demand many stages of amplification and detection, with the incident tube requirements, loss of fidelity, and'power losses. Necessarily the expense and complexity of the radio receiver is increased.

In accordance with the present invention modulated high frequency signals are directly converted into sound or similar waves bearing the modulating intelligence. This operation is made possible by the unusual and unexpected characteristic of a particular radio frequency amplifier circuit, together with the special dynamic type transducer described in further detail hereafter.

It is therefore a general object of the present invention to provide an improved electromagnetic transducer-detector capable of converting high frequency modulated signals directly to waves varying in accord with the modulating signal.

A further object of the present invention is to provide an improved amplifier-transducer combination capable of effectively converting high frequency modulated signals directly to waves varying in accord with the modulated signal.

A further object of the present invention is to provide an electromagnetic transducer-detector particularly suitable for use with an amplifier of the type defining both a cathode follower and a conventional amplifier.

Another object of the present invention is to provide an improved electromagnetic transducer-detector utilizing a two winding transformer.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the ap pended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in which:

Figure l is a schematic diagram of a complete radio receiver constructed in accordance with the principles of the present invention;

Figure 2 is a cross-sectional view with parts in elevation showing an electromagnetic transducer constructed in accordance with the present invention;

Figure 3 is an enlarged fragmentary cross-sectional view through axis 3-3, Figure 2;

Figure 4 is an illustrative diagram showing the mode of operation of the apparatus of the present invention;

Figure 5 is a greatly enlarged fragmentary view of a modified form of the transducer-detector of the present invention; and Figure 6 is an alternative embodiment of the present invention utilizing a two winding transformer.

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Referring now to Figure 1, there is shown diagrammatically at 10 a radio antenna feeding a radio frequency amplifier 12. In a broadcast receiver this amplifier might comprise one or more tuned stages using conventional type tubes. The amplifier 12 feeds the special amplifier, indicated generally at 14, which in turn energizes the transducer-detector indicated generally at 16.

The amplifier 14 is of the type using a screen grid tube and defining both a cathode-follower circuit and a conventional amplifier circuit. It includies electron tube 18, having a cathode 18a, control electrode 18b, screen electrode 18c, and anode electrode 18d. This tube may, for example, be a 50L6 type tube.

The cathode, control electrode, and screen electrode of tube 18 are connected to define a cathode follower circuit in conjunction with the winding 20. To this end, the winding 20 is connected to ground at one end and to the cathode 1811 at the other end. Resistor 22 and capacitor 24 cause no significant voltage drop at signal frequencies but provide unidirectional positive cathode bias in the usual manner. The control electrode 18b is connected to amplifier 12 by capacitor 26 and to the winding or coil 20 by the resistance 28. The latter may be of the order of /2 megohm.

The cathode, control electrode, and anode of tube 18 are connected to define a conventional amplifier in conjunction with coil 30. That is, the output voltage from this portion of the circuit appears across an impedance element (coil 30) which may be tuned to resonance with modulated carrier frequency, not in the control electrode circuit. To this end, the coil 30 is connected between anode 18d and the unidirectional cathode-anode space path voltage source 32.

Capacitor 34 is connected between the common terminal of screen and coil 30 to by-pass signal currents to ground.

As is described in further detail hereafter, the windings 20 and 30 are magnetically linked and are poled in phase opposition. That is, the feedback associated with the operation of these windings is degenerative.

The electromagnetic transducer-detector defines a voice coil 36 movably mounted and in magnetic linkage with the coils 20 and 30. This coil is short circuited through the rectifier 38 which permits only unidirectional current flow therethrough, giving rise to detector action.

The construction of the transducer-detector 16 is best seen in Figures 2 and 3. As shown, a magnetic yoke 40 of soft iron or similar magnetic material has a bottom portion 40a defining a cup shaped member in conjunction with the side wall 40b. A pair of spaced annular magnetic plates 40c and 40d extend inwardly from the edge of the cup as shown. The plates 40c and 40d have aligned circular cut-out portions as shown. A magnetic center post 40e extends upwardly frombottom 40a to approximately the position of plates 40c and 40d to define an annular air gap as shown.

A voice coil 36 is movably mounted in the annular air gap defined by the plates 40c and 40d and the post 40e. This coil is physically aflixed to the light weight sleeve 42 which encircles post 40:: at its upper portion adjacent the plates 40c and 40d. The sleeve 42 is attached to the speaker cone 44 by the corrugated flexible tube 46. The latter has a sufiicient degree of resiliency to return coil 36 to an aligned position with the plates 40c and 40d in the absence of any current flow. It also limits the amplitude of voice coil movement in response to current flow.

The coils 20 and 30 are spirally wound in the annular space defined by plates 40c and 40d and are coaxial with the voice coil 36. An insulated spacer sheet 48 separates these coils.

While only one layer of turns in coils 20 and 30 is shown in Figure 2, it will be understood that many layers may be used and that coil 20 is a relatively low impedance coil as compared to coil 30.

Cone 44 is fixedly supported at its outer periphery by means not shown. This supports the sleeve 42 and voice coil 36.

The operation of the mechanism of the present invention may be understood by reference to the diagram of Figure 4. In that diagram the modulated high frequency voltage 50 appears at antenna and at the output of amplifier 12. Current flows in windings 20 and 30 in accord with this voltage. This current flow induces a voltage in voice coil 36 having a similar wave shape.

The voltage of wave shape like wave 50 induced in the voice coil 36 can only produce unidirectional current flow because of the rectifying action of rectifier 38. This current flow is of the wave shape 52, Figure 4. Since the force acting upon the voice coil is determined by this current How, the voice coil is forced in one direction to a greater or lesser degree in accord with the modulated amplitude of the original wave 50.

The inertia of the voice coil assembly including coil 36, rectifier 38, and the sleeve 42 is very great in relation to the period of the high frequency waves and the force developed by current fiow in the coil. Consequently the voice coil is unable to follow the rapid variations in the applied force associated with current fiow 52. The voice coil movement accordingly follows the relatively smooth curve 54 corresponding to the original modulating intelligence carried by the wave 50. Sound waves in accord with this intelligence are accordingly produced.

It will be observed that the detector or demodulator action associated with transducer 16 is caused by the mechanical inertia of the voice coil 36 and associated moving parts. This is in contrast to the action of conventional detectors where no moving parts are used and electrical elements smooth out the unidirectional half wave high frequency pulses.

The rectifier 38 may be of relatively small power capacity because of the relatively small power in the voice coil 36. Consequently, it may conveniently be of the selenium, copper oxide, or similar type carried by the voice coil itself and moving in unison therewith. In the modified form of the invention shown in Figure 5, the rectifier is integrated with the single turn voice coil 36a by using a boundary layer type rectifier 36b formed integrally with the single turn. This rectifier may, for example, be of the copper oxide type with a copper oxide layer extending across the butt joint between the abutting edges of the single turn.

I have discovered that the electromagnetic transducer detector of Figure 2 is particularly suitable for use with a radio frequency amplifier using the circuit shown in Figure 1. This unanticipated result is believed to be the consequence of coaction between the amplifier and the transducer-detector that prevents the highly non-linear rectifier load associated with the detector from reacting back on the amplifier to produce an intolerable degree of distortion and intolerably low power output.

The transducer-detector of Figure 2 may be used with a conventional type amplifier but with such an amplifier it has the disadvantage of requiring a high power amplifier and low efficiency operation.

A magnetic field of constant intensity is created across the annular air gap 41 by any suitable means. This field may, for example, be created by using a permanent magnet as the post 402, as indicated by the plus and minus signs in Figure 2. Alternatively, a suitable winding en ergized by direct current flow of constant value may encircle post 402 to create this field.

Figure 6 shows a modified form of the present invention wherein the windings 36 and 20 are combined in a single winding 36a. This eliminates the necessity of a third transformer winding and, as pointed out in my copending patent application entitled High Fidelity Amplifier Requiring Low Driving Voltage, S. N. 108,717, filed August 5, 1949, now abandoned, the quality of the resultant sound is greatly improved. In the structure of Figure 6 the rectifier 38a is connected directly in the cathode circuit of the electron tube 18.

In the circuit of Figure 6 the polarity of the rectifier 38a is chosen so that the unidirectional cathode current flow of tube 18 flows through the rectifier 38a. When so connected, the unidirectional current flow through the tube 18 exerts no magnetizing effect on the magnetic core by reason of the connection of the coil 36a. This provides an advantage over conventional output transformers where the unidirectional electron tube current fiow passes through the transformer windings and tends to saturate the core, thus introducing distortion. One advantage of the structure of Figure 6 as distinguished from the structure of Figure 1 resides in elimination of this magnetizing current by the rectifier 38a. The magnetic structure can therefore be made smaller without increasing dis tortion.

The magnetic structure used with the form of the transducer-detector of Figure 6 is like that of Figure 2 except that the separate winding 20 as shown in Figure 2 is omitted or replaced by additional turns of the winding 30 and the winding 36a is wound on the sleeve 42 rather than the winding 36. The rectifier 38a may be mounted on the sleeve 42 or may be separately mounted as desired.

If desired, the resistance 28, Figures 1 and 6, may be connected directly to ground rather than to the resistance 22.

While I have shown and described specific embodiments of my invention, it will of course be understood that I do not wish to be limited thereto and that by the appended claims I intend to cover all variations and alternative constructions falling within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electromagnetic transducer-detector comprising in combination, a magnetic yoke defining a substantially annual non-magnetic gap, a voice coil movably positioned in the gap, a rectifier, means connecting the rectifier to the coil to cause unidirectional current flow therethrough, means operative to produce a unidirectional magnetic flux across the gap, and a coil substantially coaxial with the voice coil adapted to carry modulated high frequency current.

2. An electromagnetic transducer-detector comprising in combination, a magnetic yoke defining a substantially annular non-magnetic gap, a voice coil movably positioned in the gap, a rectifier, means connecting the rectifier to the coil to cause unidirectional current flow therethrough, means operative to produce unidirectional magnetic flux across the gap, the yoke having substantially fiat annular portion adjacent the gap, and a coil substantially coaxial with the voice coil and substantially in the plane of the annular portion of the yoke adapted to carry modulated high frequency current.

3. In combination, a high frequency amplifier comprising an electron tube having cathode, anode, control, and screen electrodes, a pair of magnetically linked coils, means interconnecting the cathode, control electrode, anode and one of the coils to define a conventional amplifier, means interconnecting the cathode, control electrode, screen electrode and the other of the coils to define a cathode follower, a third coil movably mounted and magnetically linked with the first coils, a rectifier, means defining a circuit including the third coil and the rectifier to cause unidirectional current fiow therein, and means operative to produce a unidirectional magnetic flux linking the third coil.

4. In combination, a high frequency amplifier comprising an electron tube having cathode, anode, control electrode and screen electrode, a pair of spiral adjacent substantially coaxial coils, means interconnecting the cathode, control electrode, anode and one of the coils to define a conventional amplifier, means interconnecting the cathode, control electrode, screen electrode and the other of the coils to define a cathode follower, a magnetic yoke defining a substantially annular non-magnetic gap adjacent the inner turns of the coils, a third coil movably mounted in the gap, a rectifier, means defining a circuit including the third coil and the rectifier to cause unidirectional current flow therein, and means operative to produce a unidirectional magnetic fiux linking the third coil.

5. In an electromagnetic transducer-detector of the type defining a substantially annular non-magnetic gap, the im provement comprising a coil movably mounted in the gap, a rectifier mounted for movements in unison with the coil connected thereto to cause unidirectional current flow therethrough, and means to produce unidirectional magnetic field in the gap.

6. An electromagnetic transducer-detector comprising in combination, means defining a magnetic circuit having a non-magnetic gap, a voice coil movably mounted in said gap, a rectifier connected across the voice coil, a pair of coils substantially coaxial with the voice coil, an electron tube, means defining a cathode follower circuit using one of said last coils and the tube, and means defining a conventional amplifier utilizing the other coil and the tube.

7. In combination, a receiver for high frequency modulated current, an amplifier for said current, a transducerdetector including a magnetic yoke defining an annular non-magnetic gap, a voice coil movably positioned in the gap, a rectifier connected in circuit with the voice coil to cause unidirectional current flow therethrough, the yoke being magnetized to produce unidirectional flux across the gap, and a coil coaxial with the voice coil and substantially in the plane of the voice coil and connected to the amplifier to carry the amplified modulated high frequency current.

8. In combination, a receiver for high frequency modulated current, an amplifier for said current, a transducerdetector including a magnetic yoke defining an annular non-magnetic gap, a voice coil movably positioned in the gap, a rectifier connected in circuit with the voice coil to cause unidirectional current flow therethrough, the yoke being magnetized to produce unidirectional flux across the gap, the yoke having a substantially fiat annular space therein around the gap, and a winding in said space connected to the amplifier to carry the amplified modulated high frequency current.

References Cited in the file of this patent UNITED STATES PATENTS 1,795,948 High Mar. 10, 1931 1,923,831 Juhasz Aug. 22, 1933 1,931,236 Nicolson Oct. 17, 1933 1,971,630 Von Suchorzynski Aug. 28, 1934 2,056,824 Cawley Oct. 6, 1936 2,319,627 Perlrnan May 18, 1943 2,328,836 Moynihan Sept. 7, 1943 2,429,124 Cunningham Oct. 14, 1947 2,475,641 Rosenberg July 12, 1949 2,494,918 Volkers Jan. 17, 1950 FOREIGN PATENTS 326,296 Great Britain Mar. 13, 1930 

